The honeybee produces honey and beeswax and plays a vital role in crop production through pollination. (Photo: Creative Commons)

German physicist Albert Einstein once warned that should honeybees disappear, so would our global food supply. "No more bees ... no more men," he said.

Colony collapse disorder, or CCD, describes the vast and mysterious dying off of U.S. honeybees. The U.S. Department of Agriculture, or USDA, reports that honeybees are disappearing in large numbers and that no one really knows why it's happening.

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"[CCD] is a serious problem threatening the health of honey bees and the economic stability of commercial beekeeping and pollination operations in the United States," the USDA reports.

The main symptom observed in honeybee populations affected by CCD is a very low, or even no, adult honeybee presence in the hive and no dead bodies present. The mystery of where the missing honeybees have gone is at the root of the CCD honeybee epidemic in the U.S.

The Agricultural Research Service, the research branch of the USDA, reports that the U.S. honeybee colony population fell 21.9 percent nationwide between 2011 and 2012. While this figure is lower than it was in previous years -- honeybee colony populations declined by 30 percent between 2010 and 2011 and 29 percent between 2008 and 2009 -- scientists are most worried about the fact that the bees are disappearing with no trace of where they've gone. From Time:

On normal years, commercial beekeepers might expect to lose 10% to 15% of their colony, but over the past five years, mortality rates for commercial operations in the U.S. have ranged from 28% to 33%. Since 2006 an estimated 10 million beehives worth about $200 each have been lost, costing beekeepers some $2 billion. There are now 2.5 million honeybee colonies in the U.S., down from 6 million 60 years ago.

According to the USDA, bee pollination is responsible for more than $15 billion in increased crop value each year -- the equivalent of about one mouthful in three in our diet. Almonds, berries, avocados, peppers, coconuts, tomatoes, coffee, cocoa, fruits and vegetables rely on honey bees for pollination. The almond industry in California alone requires 1.4 million honeybee colonies just to maintain itself.

Scientists first identified CCD in 2006 when some U.S. beekeepers reported unusually high losses of up to 90 percent of their honeybee colonies. While beekeepers have reported unusual honeybee colony losses before -- in 1903, 2,000 honeybee colonies in Utah disappeared under mysterious circumstances -- the recent disappearance of honeybees is most alarming because there is no clear pattern as to why it's happening.

There are four areas scientists are studying to try and determine the cause of CCD:

Pathogens Scientists are not ruling out the possibility that some deadly bee virus or bacteria is wiping out our bees. The lineup of possible offenders includes Nosema, a fungal parasite that affects the honeybee's gut, and Israeli acute paralysis virus, among other potential pathogens.

Parasites In colonies affected by CCD, varroa mites, which cause a deadly disease in bees called varroatosis, are often found to be present in the hives. However, researchers can't find a clear link between the mites and CCD.

Managementstressors Honeybees in the U.S. agriculture industry are constantly being moved from one location to another. One theory is that the stress of being in constant flux, coupled with apiary crowding, might be causing CCD.

Environmental stressors Some honeybee colonies are unintentionally exposed to pesticides. This, along with pollen scarcity and limited access to water, is thought to be one of a number of environmental factors that could be causing CCD. One study from 2010 even purports that cell phone radiation is screwing up the honeybees' ability to navigate.

Let's say Einstein was right, and the honeybee population really is going to disappear. Will man also perish?

The good news is, it's not that cut and dry. According to an article from the Telegraph, the doomsday scenario of a vanishing global bee population is overblown. Corn, wheat and rice, all staples of the human diet, are all pollinated by wind, not bees.

Also, keep in mind that honeybees are not even native to North America (they were brought here by European settlers); here are a number of other indigenous species, including moths and butterflies, that can pollinate crops.